Reply to Thread

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.

User Name:

Password

Please enter a password for your user account. Note that passwords are case-sensitive.

Password:

Confirm Password:

Email Address

Please enter a valid email address for yourself.

Email Address:

Log-in

User Name

Remember Me?

Password

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options

Miscellaneous Options

Automatically parse links in text

Automatically embed media (requires automatic parsing of links in text to be on).

Automatically retrieve titles from external links

Topic Review (Newest First)

10-03-2012 12:09 PM

oldbogie

Quote:

Originally Posted by sherri32

My son has a 1991 Chevrolet silver-ado with a 350 vortech engine ( i am a mother and don't know anything about vehicles LOL) I bought his truck from a man who let it sit up about 5 years, when we first got the truck we put a new alternator, battery, spark plugs and wires and a new fuel pump on it. The truck ran fine for about 2 months and then one day on his way home from work. He turned off the interstate and it died. He finally made it home and I took it to a mechanic who said his number 1 and number 8 cylinders are not firing and he needs a new engine. The truck does not smoke and runs fine until it gets hot then it acts like it wants to shake when you put it in gear. My ? is does anyone know anything about this or if this has happened to them or is the mechanic right and he need a new engine? What should I do? My son is only 17 and knows nothing about cars either so i'm stumped as do i put money in this or just give up and try and buy something else.

If this engine is original to the truck it is an LO5, these are 350 cubic inches that use Swirl Port heads with Throttle Body Injection (TBI).

If the Check Engine Light (CEL) is illuminated there will be code information that can be down loaded from a connector on the bottom of the instrument panel. Go to this web site for instructions to use the connector and the CEL light to read the codes without a code reader tool: >>> How to read older GM OBD diagnostic codes for free >>>.

Go to this web site to get the list of GM OBD 1 codes: >>> OBD-1 Diagnostic Trouble Codes >>>. OBD 1 stands for On Board Diagnostics (generation) 1. This is used from about 1984 through 1995 for models with electronic fuel injection of which TBI is one of several types.

New fuel pump if this still has TBI the pump is in the fuel tank and is a pretty large effort to replace, is that what you did or had done? A fuel pump on the side of the engine, forward on the passenger side, would indicate the engine has either been replaced and the fuel system modified to a carburetor, or the existing engine was similarly modified to accept a carburetor.

Cylinders 1 and 8 are at opposite ends of the engine, 1 being the front driverís side and 8 the rear passenger side. However they follow each other in firing order (1,8,4,3,6,5,7,2), this is how the distributor cap should be wired. The rotor within the cap rotates clockwise when viewed from above, which of course is the only view of it you're going to get.

One of the risks with the Chevy Small Block is wear and loss of cam lobes where flat tappet cams are used which is what is found in the vast majority of pre-1996 pick-ups. There is always the possibility that you mechanic has diagnosed this and this could be the reason he recommends engine replacement. This is easy to check for by removing the rocker covers to watch the amount of valve action, little compared to the others would indicate a wiped out cam lobe and tappet.

A truck this old could be having problems with the timing chain and gears. This allows the cam to fall out of synchronization with the crankshaft. But this is a problem well leave for another day.

The 1 and 8 spark plug firing problem if real could be in the distributor cap. First check to see that the plug wires are pushed tightly into the cap. Then inspect their lengths for damage. Running the engine in the dark and looking for electrical arcs is one way of isolating high voltage leaks as you can see them. Given that 1 and 8 are next to each other on the cap terminals there could be arcing between them inside the cap. Removal of the cap and careful inspection will show trails that look a lot like a crack in the plastic. Part of the tune up for the HEI ignition should include a cap and rotor as the high energy of these systems erodes the contacts.

Check engine vacuum, this is a pretty mildly cammed engine so it should be high certainly above 16 inches at idle and steady. A vacuum check is a good diagnostic to isolate problems. Follow this link for more detail: >>> How to Use and Interpret a Vacuum Gauge >>>.

I'd highly recommend purchasing a service manual for this truck. The common over the counter manuals from Haynes or Chiltonís are reasonably priced and contain a wealth of information.

Bogie

10-02-2012 07:49 PM

sherri32

The truck starts really good and sounds good when it is in park. Once you put it in gear it starts shimming and sounding like it's going to fall apart

10-02-2012 07:43 PM

sherri32

Thank you all for your responses! I bought the new distributor cap and button thingy and tried that and still, it's the same. I put some fuel injection cleaner in the gas tank and still the same. Just acts like it is not getting enough power. This is getting so frustrating for me.

09-24-2012 12:08 AM

cdminter59

Help with engine

I have done several Google searches on your problem. You really need someone that can check computer codes as well as other sensors. There is a few checks you can do. Use a can of carburetor cleaner with the engine running, spray along the intake manifold where it bolts to the engine block. Also spray along the throttle body where it bolts to the intake manifold. You are looking for vacuum leaks. if you have a leak the engine will speed up. The coolant temp sensor has to be checked with a digital ohm meter. This should show a reading of 200 ohms or more. If not replace it. IAC-Idle Air Control has to be checked by a dealer. It can be taken off and use carburetor spray to clean the carbon off of it. Spray inside the hole where it bolts up too. The fuel pump pressure needs to be checked. It should have 13-15 lbs and rev the engine to see if pressure drops. Replace the fuel filter under the cab of the truck on the inside of the frame rail. The EGR Valve and the EGR solenoid need to be checked. There is a possibility you may have got gas with water in it. Get a bottle of Chevron Fuel System Cleaner and a bottle of water remover and pour into gas tank. Just drive it around the block a couple of times to see if it clears up.

09-23-2012 05:42 PM

RWENUTS

Plus don't forget about youtube. Lots of good instructional vids there too!

09-23-2012 04:55 PM

lmsport

That year truck was known to have failure of the reluctor in the distributor.
The International Automotive Technicians Network is the largest network of automotive repair professionals in the world

I really don't trust my mechanic...LOL I live in a small town and he is the only one around who does mechanic work. So I think he is trying to make money off of me and if he doesn't need a new engine that would be so sweet. He said the number one and number eight were loosing compression, but when I put it in gear it wants to shake or shimmy and then when it does run awhile it dies. I'm not sure about the motor if they didn't come out till 96 then it would have to of been replaced before. My son loves this ugly truck and if i can get out with less than 200.00 by fixing it, that would be nice. But if we need a new motor I just can't go that route. I will pick up a distributor cap one day this week and try to put it on my self...I'm sure it can't be that hard, right? And hopefully that will work. If not i'll go from there. Thank you all for your responses.

09-22-2012 08:01 PM

RWENUTS

X3.
Find a better mechanic.
THe firing order for your truck is 18436572. As you see 1 and 8 are side by side on the distributor cap. Could be just a cracked cap.

09-22-2012 07:26 PM

BOBCRMAN@aol.com

Get another opinion from a trusted (ask around) private garage. It could be just a bad wire/plug or headgasket or possibly a bad cylinder head.

^^^^^^^ woops slow typer. What he said also.. Bob

09-22-2012 07:22 PM

cdminter59

Help with engine

Hi, If this truck is a 1991 has it had the motor replaced before? The Vortec motors didn't come out until 1996. Well is your mechanic trustworthy. He should have done compression test on each cylinder. (everywhere there is a spark plug) If there is no fire to #1 and #8 cylinder it could be something simple as a bad distributor cap and rotor button. It also could be a bad ignition coil.

09-22-2012 06:46 PM

sherri32

Help with engine

My son has a 1991 Chevrolet silver-ado with a 350 vortech engine ( i am a mother and don't know anything about vehicles LOL) I bought his truck from a man who let it sit up about 5 years, when we first got the truck we put a new alternator, battery, spark plugs and wires and a new fuel pump on it. The truck ran fine for about 2 months and then one day on his way home from work. He turned off the interstate and it died. He finally made it home and I took it to a mechanic who said his number 1 and number 8 cylinders are not firing and he needs a new engine. The truck does not smoke and runs fine until it gets hot then it acts like it wants to shake when you put it in gear. My ? is does anyone know anything about this or if this has happened to them or is the mechanic right and he need a new engine? What should I do? My son is only 17 and knows nothing about cars either so i'm stumped as do i put money in this or just give up and try and buy something else.